In a CDMA wireless system the activation or deactivation of-a cell/sector affects the network. The sudden activation of the cell/sector causes a sudden increase in the total forward link power. This may temporarily degrade the forward link performance of the network and possibly cause the calls in other cells/sectors close to the activating cell/sector to be dropped due to the sudden increase of channel interference from the activating cell/sector. In addition, the sudden deactivation of a cell/sector will result in calls in the cell/sector being dropped. To avoid this problem, when a cell/sector is activated in a CDMA wireless system, the transmitted power of the transmitter at the base station is increased gradually, while the effective noise figure of the receiver at the base station is gradually decreased accordingly. This allows the users in the neighboring cells/sectors who are subject to the interference from the activating cell/sector to have enough time to handoff to the activating cell/sector. The synchronized gradual increase of the transmitted power and decrease in the receiver effective noise figure is known as "blossoming". Similarly, the synchronized gradual decrease in the transmitted power and increase in the receiver effective noise figure is known as "wilting". This occurs when a cell/sector is deactivated. Wilting allows the users in the deactivating cell/sector to have enough time to handoff to neighboring cell/sectors, rather than being dropped. During normal operation of the cell/sector the balance between the forward link handoff boundary and the reverse link handoff boundary must be constantly maintained. This operation, known as "breathing", is also effected by balancing the transmitted power and the effective noise figure at the receiver. In order to keep the handoff boundaries balanced, for every one dB change in transmitted power there must be an opposing one dB change in the receiver effective noise figure.
The implementation of the receiver blossoming, breathing and wilting functions has been traditionally effected in the analog chain of the receiver at the RF or at the analog IF stages by degrading its noise figure. Practically, this is traditionally effected by altering a variable attenuator located at the RF section or the early stages of the IF section, prior to any channel separation. The drawbacks of this approach are:
1. inaccurate control due to gain and/or noise figure instability (over temperature, aging, non-linearity, etc.)
2. this method is not suitable for effecting noise power regulation on a channel by channel basis in a multichannel CDMA receiver in which the channels share the same RF section and early stages of IF section.
Thus, there is a need in the industry to provide a CDMA receiver capable to implement the blossoming, breathing and wilting functions while alleviating the difficulties associated with prior art methods.